Revert "Add a specialized instruction for `.nil?` calls"

This reverts commit 9faef3113fb4331524b81ba73005ba13fa0ef6c6.

It seemed to cause a failure on macOS Mojave, though I'm unsure how.
https://rubyci.org/logs/rubyci.s3.amazonaws.com/osx1014/ruby-master/log/20190802T034503Z.fail.html.gz

This tentative revert is to check if the issue is actually caused by the
change or not.

8 files changed, 1 insertions, 48 deletions

diff --git a/benchmark/nil_p.yml b/benchmark/nil_p.yml
deleted file mode 100644
index 79ba4f2177..0000000000
--- a/benchmark/nil_p.yml
+++ /dev/null
@@ -1,9 +0,0 @@
-prelude: |
-  class Niller; def nil?; true; end; end
-  xnil, notnil = nil, Object.new
-  niller = Niller.new
-benchmark:
-  - xnil.nil?
-  - notnil.nil?
-  - niller.nil?
-loop_count: 10000000
diff --git a/compile.c b/compile.c
index 0dbefd3155..774dadfc79 100644
--- a/compile.c
+++ b/compile.c
@@ -3255,7 +3255,6 @@ iseq_specialized_instruction(rb_iseq_t *iseq, INSN *iobj)
 		  case idLength: SP_INSN(length); return COMPILE_OK;
 		  case idSize:	 SP_INSN(size);	  return COMPILE_OK;
 		  case idEmptyP: SP_INSN(empty_p);return COMPILE_OK;
-                  case idNilP:   SP_INSN(nil_p);  return COMPILE_OK;
 		  case idSucc:	 SP_INSN(succ);	  return COMPILE_OK;
 		  case idNot:	 SP_INSN(not);	  return COMPILE_OK;
 		}
diff --git a/defs/id.def b/defs/id.def
index 25677ffdc2..66dfdf915a 100644
--- a/defs/id.def
+++ b/defs/id.def
@@ -3,7 +3,6 @@ firstline, predefined = __LINE__+1, %[\
   max
   min
   freeze
-  nil?
   inspect
   intern
   object_id
diff --git a/insns.def b/insns.def
index 7c93af6e4d..c971026cf6 100644
--- a/insns.def
+++ b/insns.def
@@ -808,20 +808,6 @@ opt_str_freeze
     }
 }
 
-/* optimized nil? */
-DEFINE_INSN
-opt_nil_p
-(CALL_INFO ci, CALL_CACHE cc)
-(VALUE recv)
-(VALUE val)
-{
-    val = vm_opt_nil_p(ci, cc, recv);
-
-    if (val == Qundef) {
-        CALL_SIMPLE_METHOD();
-    }
-}
-
 DEFINE_INSN
 opt_str_uminus
 (VALUE str, CALL_INFO ci, CALL_CACHE cc)
diff --git a/object.c b/object.c
index 16dce71671..3aa7cd20d2 100644
--- a/object.c
+++ b/object.c
@@ -1687,7 +1687,7 @@ rb_true(VALUE obj)
  */
 
 
-MJIT_FUNC_EXPORTED VALUE
+static VALUE
 rb_false(VALUE obj)
 {
     return Qfalse;
diff --git a/vm.c b/vm.c
index b4e2e3c5e6..115bdca503 100644
--- a/vm.c
+++ b/vm.c
@@ -1656,7 +1656,6 @@ vm_init_redefined_flag(void)
     OP(Call, CALL), (C(Proc));
     OP(And, AND), (C(Integer));
     OP(Or, OR), (C(Integer));
-    OP(NilP, NIL_P), (C(NilClass));
 #undef C
 #undef OP
 }
diff --git a/vm_core.h b/vm_core.h
index d5e18ba489..0120f21831 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -550,7 +550,6 @@ enum ruby_basic_operators {
     BOP_LENGTH,
     BOP_SIZE,
     BOP_EMPTY_P,
-    BOP_NIL_P,
     BOP_SUCC,
     BOP_GT,
     BOP_GE,
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 1875d35de1..57f6d91e88 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -4228,26 +4228,6 @@ vm_opt_empty_p(VALUE recv)
     }
 }
 
-VALUE rb_false(VALUE obj);
-
-static VALUE
-vm_opt_nil_p(CALL_INFO ci, CALL_CACHE cc, VALUE recv)
-{
-    if (recv == Qnil) {
-        if (BASIC_OP_UNREDEFINED_P(BOP_NIL_P, NIL_REDEFINED_OP_FLAG)) {
-            return Qtrue;
-        } else {
-            return Qundef;
-        }
-    } else {
-        if (vm_method_cfunc_is(ci, cc, recv, rb_false)) {
-            return Qfalse;
-        } else {
-            return Qundef;
-        }
-    }
-}
-
 static VALUE
 fix_succ(VALUE x)
 {